The overall goal of this multi-PI proposal is to investigate the role of naturally occurring IgM anti-leucocyte autoantibodies in inhibiting inflammatory processes that occur after ischemia-reperfusion injury (IRI). We and others observed that a subset (30%) of patients with high levels of IgM-ALA had minimal or no rejections after a kidney or heart transplant. We showed that IgM-ALA bind to leucocyte receptors in a highly specific manner and at body temperature does not cause leucocyte cell death despite presence of complement. Furthermore, we showed that IgM-ALA (i) bind to CD4 and CD3 receptors (but not HLA, IL-2R) and inhibit T cell activation, proliferation and production of certain proinflammatory cytokines (TNF-1, IL-2) but not others (IL-6 and IL-8), (ii) bind to chemokine receptors and inhibit chemotaxis. Based on these findings we questioned whether IgM- ALA downregulate inflammation that accompanies renal IRI. Glycolipids released after ischemic injury are processed and presented by resident dendritic cells (DC), in presence of cytokines, to NKT cells, which get activated and produce cytokines (in particular IFN?) to amplify the inflammatory process by attracting and activating leucocytes from the systemic circulation. We posit that IgM-ALA could downregulate the inflammatory process by binding to receptors involved in cell activation and inhibiting leucocyte chemotaxis. To test our hypothesis, we used mice deficient in IgM (IgMko mice) and showed that these mice develop severe renal IRI relative to their WT-B6 counterparts. We propose 3 aims: Aim 1 will test the hypothesis IgM-ALA is protective in renal IRI. To test this hypothesis we plan to perform renal IRI in IgMko mice and rescue them with purified B1 cells (source of IgM-ALA in WT mice) and also with purified plasma IgM, obtained from WT mice. We will also test the therapeutic value of IgM by administering IgM to WT mice. Aim 2 will test the hypothesis that the enhanced inflammatory process causing more severe renal IRI in mice deficient in IgM results from lack of IgM mediated inhibition of cells in the dendritic cell (DC)/natural killer T (NKT) cell pathway as well as the downstream IL17 pathway and not from some other mechanism that is unmasked in mice deficient in IgM. We will interrupt this pathway in IgMko mice with blocking antibodies and depleting DCs with diptheria toxin. Aim 3 will test the hypothesis that IgM-ALA inhibits the inflammatory process by binding to cell receptors and attenuating the function of DC and NKT cells and chemotaxis and function of leucocytes. The significance of the studies proposed is that it was observations in humans that undergird the hypothesis that naturally occurring IgM-ALA might abrogate inflammation associated with acute kidney injury (AKI). Our preliminary data provide strong evidence that indeed these naturally occurring IgM-ALA are protective in AKI and thus these studies will define mechanisms of tissue protection by naturally occurring IgM-ALA.